1. Field of the Invention
The present invention is directed to a separation process for an oxidized liquid effluent mixture from a subcritical wet oxidation process and, more particularly, to a two-stage separation process for separating the oxidized liquid effluent mixture.
2. Description of the Related Art
Wet oxidation is well known for the treatment of aqueous wastewaters. The process generally involves heating a mixture of the wastewater and an oxygen-containing gas to effect oxidation of oxidizable substances contained in the wastewater. When air is used as the source of oxygen-containing gas, the wet oxidation process is generally referred to as "wet air oxidation."
Generally, subcritical wet oxidation systems include a wet oxidation chamber followed by a single separator vessel, with a pressure control valve therebetween to maintain the oxidation chamber pressure. When the oxidation process is terminated, an oxidized effluent mixture traverses the pressure control valve to the separator vessel. The pressure drop between the wet oxidation system and the separator vessel causes the mixture to separate into an oxidized liquid effluent and a gaseous phase.
Low pressure separators generally operate at, or near, ambient pressure. If a single low pressure separator vessel follows the wet oxidation system, the oxidized liquid effluent is generally acceptable for downstream processes (such as for pumping, or for storage in tanks). However, the gaseous phase produced from a single low pressure separation vessel is disadvantageous because it is at a low pressure, and requires additional equipment and energy to transport to downstream processes. In some instances, the gaseous phase may require further treatment, and potentially the expenditure of significant amounts of energy and expense for transport to and through subsequent treatment processes. Moreover, the gaseous phase from a single low pressure separator vessel generally contains a significant amount of water vapor. The water vapor also adds expense to downstream treatment of the gaseous phase, for example, increasing the energy requirement in a high temperature afterburner. Condensation of the water vapor on the interior of equipment may also cause corrosion to the equipment that comes into contact with the gaseous phase.
High pressure separators generally operate in the range of about 50 to 100 psig. If a single high pressure separation vessel is used, the energy expenditure for moving the gas would be eliminated, as the gaseous phase would retain sufficient pressure to provide the motive force to be transported to another location. However, in this instance, the oxidized liquid effluent may not be suitable for discharge to downstream processes, because the over pressure may cause a significant amount of gases, including CO.sub.2, N.sub.2, and O.sub.2, to remain dissolved in the oxidized liquid effluent. When such as oxidized liquid effluent is stored in a low pressure covered collection tank, for example, the dissolved gases remaining therein will come out of solution and collect within the talk, causing operational problems. Several techniques associated with various high pressure or temperature processes, including wet oxidation, are reported below.
U.S. Pat. No. 3,150,105 discloses a blow down talk to receive cooled regenerated carbon slurry from a wet oxidation reactor.
U.S. Pat. No. 3,994,702 discloses a flooded sluicing chamber for ash removal from a pressurized gasification chamber.
U.S. Pat. No. 4,620,563 discloses a blowdown pot with an inlet pressure control valve through which the pot receives unwanted residue e.g., ash from a high pressure chemical reactor.
U.S. Pat. No. 5,011,114 discloses a pressure control valve with a valve seat and support assembly extending beyond the valve body to prevent erosion by the blowdown slurry.
U.S. Pat. No. 5,389,264 discloses a process for dissipating the energy of a wet oxidation mixture and preventing erosion of the phase separator vessel after that stream traverses a pressure control valve.
A need remains, however, for an improved process for providing an essentially gasfree oxidized liquid effluent with a gaseous phase with a reduced water vapor concentration, from a subcritical wet oxidation system. Lastly, there is a need to reduce or eliminate the energy requirement for transporting the gaseous phase to further treatment.